Bandwidth

[smartin]

Hi everybody,

Could somebody help me with the bindwidth concept?
Which bindwidth is correct for a wavelenght of 280nm? How is bindwidth value going to influence on the final chromatogram?

Thanks,

[lmh]

It probably won't affect anything very much, within reasonable ranges. UV absorbances tend to be fairly broad peaks; probably a thing absorbing at 280nm actually has significant absorbance all the way from 250/260 to 300/310, so whether you look at a range from 265-295, or a range from 279-281 won't matter.

If you use a very very broad range, you will lose a little selectivity, and other peaks will appear in your chromatogram (things that absorb at 230 or 240nm will begin to have an effect). If you use a very, very narrow range, you are actually relying on a smaller amount of light (in a PDA, a smaller number of light-sensitive-elements) and the noise will increase slightly. I usually default to about 9nm width, but it depends on your detector.

[pharmaguy]

Just to expand on Imh's explanation. Bandwidth sets the range around a given wavelength that the detector will look at and report on the chromatogram. Allowing a broader range will detect compounds that may absorb at much different wavelengths from your target to be seen.